This application is 35 U.S.C. xc2xa7 371 of PCT/JP98/05370, filed Nov. 30, 1998
The present invention relates to an intraocular lens and a process for the production of a one-piece intraocular lens. More specifically, the present invention particularly relates to a one-piece intraocular lens which can be inserted through a small incision by bending its optic portion when it is inserted into an eye, a process for the efficient production of the same, and a soft intraocular lens which permits the prevention of deformation of a soft optic portion caused by the shrink of a capsule after intraocularly inserted.
In recent years, with an increase in the population of aged people, senile cataract patients are distinctively increasing. A treatment against cataract is carried out by removing a clouded nucleus and cortex of a crystalline lens and either correcting a vision with an eyeglass or a contact lens or inserting an intraocular lens, while it is general practice to employ a method in which a crystalline lens as a whole is removed and an intraocular lens is fixed.
The above intraocular lens comprises an optic portion which functions as a substitute lens for the crystalline lens removed due to cataract and a narrow and long filament-like haptic portion which is to fix and hold the optic portion in the central position in a capsule. It is known that the above intraocular lens includes an intraocular lens of a type which is formed by separately producing the haptic and optic portions and later combining them (sometimes called two-piece or three-piece type), and a one-piece intraocular lens formed by integrally producing the haptic and optic portions (sometimes called one-piece type). As a material for the optic portion, there has been mainly used polymethyl methacrylate (to be referred to as xe2x80x9cPMMAxe2x80x9d hereinafter) which is a hard material. The reason for the use of PMMA as a material for the above planting intraocular lens is that it is transparent and excellent in stability in organisms (biocompatibility) and that it has adequate machinability and can provide elaborate lenses stably. As a material for the hepatic portion for holding the above optic portion formed of PMMA, for example, a mono-filament of PMMA, polypropylene or polyimide has been used. Concerning the bonding of the above optical portion and haptic portion, as one type, a small hole for attaching the haptic portion is made in the optic portion, the haptic portion is inserted in the small hole after the optic portion is completed, then the haptic portion is fixed to the optic portion by staking or laser (two-piece or three piece type), or there is a one-piece type integrally formed of PMMA.
On the other hand, with a widened use of an ultrasonic emulsification aspiration method in recent years, there has been developed an intraocular lens which can be inserted through a small incision, for decreasing postoperative astigmatism and an operation stress. That is, the above intraocular lens is formed of a soft material as a material for the optic portion so that it can be bent so as to be inserted through a small incision.
Since, however, the soft material is difficult to machine, i.e., cut and polish unlike a conventional PMMA, the production of the optic portion generally uses a cast-molding method in which a monomer, a prepolymer or an oligomer as a material for forming the optic portion is polymerized in a mold. Further, since it is also difficult to mechanically make a small hole in the method of attaching the haptic portion, it is required to employ a method different from the conventional method.
For producing the above soft intraocular lens, various method, for example, shown below have been so far proposed.
(1) A method of producing an intraocular lens having an easily-non-removable haptic portion, in which the end portion of a filament constituting the haptic portion is permanently deformed to form a mechanical engagement portion having the form of a bulb, etc., or another filament having a mechanical engagement portion is bonded to the end of the former filament to form a terminal portion of the haptic portion and an optical member is mold-shaped with the terminal portion inserted (JP-A-62-142558, JP-A-62-152450).
(2) A method of producing an intraocular lens, in which a soft optical material is polymerized in a mold, then, a mold with a polymerized soft optical material in it is cooled to harden the soft material, a small hole in which a haptic portion is to be inserted and a small hole in which an anchor filament is to be inserted are mechanically made in the optic portion, then, the haptic portion is inserted in the haptic-portion-inserting small hole, a filament formed of the same material as that of the haptic portion is inserted in the anchor-filament-inserting small hole, an intersection of the haptic portion and the anchor filament is irradiated with a laser beam to fuse the haptic portion to the hole, and further, irradiation with a laser beam is effected along the inserting holes (JP-A-4-292609).
(3) A method of producing a foldable intraocular lens, in which a rod of a homopolymer or a copolymer of 2-hydroxyethyl methacrylate (HEMA) was prepared as a foldable optical member, the rod is placed in a tubular mold, a haptic portion is formed around the rod by polymerizing a hard material such as PMMA, then, a disc is obtained by cutting the rod, ground and polished to produce an intraocular lens and the lens is hydrated (allowed to contain water) (JP-A-4-295353).
(4) A method in which a flat plate is prepared from a crosslinked acrylic resin material, placed on a holder and cut into a disc with a lathe at a low temperature, the disc is cut to form a soft optic portion and then the soft optic portion is provided with haptic portions to obtain a three-piece type intraocular lens, or the above flat plate is cut into a material in the form of a lens to obtain an intraocular lens having a foldable optic portion and a soft haptic portion formed of the same soft material as the material of the optic portion (JP-A-1-158949).
(5) A method of producing an intraocular lens, in which an optical material having a diameter of 5 mm and a height of 20 mm was prepared by polymerization and then placed in the center of a cylinder having an inner diameter of 15 mm and a height of 20 mm, a monomer for forming a material of a haptic portion is polymerized in a circumferential portion thereof, and then, a material in the form of an intraocular lens is prepared by cutting and immersed in an alcohol for about 48 hours to soften the optic portion by esterification (JP-A-5-269191).
However, the above methods of producing intraocular lenses all have defects that the procedures are complicated and that the production efficiency is poor. That is, in the above method (1), it is required to make a plastic filament which is to form the haptic portion into a complicated form. The filament which is to form the haptic portion has a diameter of approximately 0.15 mm, and it is required to provide an extremely complicated and fine step for making the end portions of all the filaments in one form by melting the under heat. The haptic portion is required to have a form suitable for holding and fixing in an eye, and the form thereof is elaborately made by thermoforming. That is, when a soft optical material is produced in a mold so as to surround the above elaborately made haptic portion, the haptic portion is again exposed to heating and pressing steps, and the form and dimensions thereof may be altered.
In the above method (2), it is required to cool the material and make two holes, the hole for inserting the haptic portion and the anchor-filament-inserting hole which intersects with the former hole, and it is also required to insert the haptic portion and the anchor filament in the holes and attain the fusing of the haptic portion and the filling the hole with filament by repeatedly irradiating them with laser beam. Therefore, considerably complicated procedures are required.
In the above method (3), the optic portion is formed of a material composed mainly of HEMA, and a lens at the time of cutting is hard, but it is made soft by hydration after the cutting. HEMA shows a difference in water absorptivity from one lot to another, and it is difficult to maintain constant performances of intraocular lenss. Further, it takes a time during an operation to hydrate the intraocular lens, and further, when an intraocular lens is hydrated in advance, it is difficult to the intraocular lens in a sterile state.
Further, in the above method (4), the material of the haptic portion is the same as the material of the optic portion, and the haptic portion is therefore soft. The haptic portion of a conventional intraocular lens has a diameter of approximately 0.1 to 0.2 mm, and the haptic portion is considerably soft. It is therefore thought that maintaining an haptic portion angle is difficult and that the positional stability of the optic portion in a capsule is difficult.
In the above method (5), no haptic portion material having reactivity with an alcohol can be used. It is therefore not possible to use PMMA which is generally used at present.
Further, a chemical reaction is caused on the optic portion after the form of an intraocular lens is made by precision cutting and polishing, and the form of the optic portion (change in curvature, thickness, optical radius, etc.) may be changed, and it is difficult to maintain the haptic portion angle during processing.
Meanwhile, when the optic portion and the haptic portion are bonded in a two-piece or three-piece intraocular lens, an angle is provided in quite a few cases such that the haptic portion forms an angle of approximately 5 to 10 degrees with a plane at right angles with the optical axis of the optic portion. The above is for stable registering after the lens is fitted in a capsule.
Further, in the above one-piece type intraocular lens, the optic portion and the haptic portion are integrally formed in many cases. FIG. 7 shows a plan view of a conventional one-piece intraocular lens. FIG. 8 schematically shows a side view of the haptic portion of a conventional one-piece intraocular lens. In these Figures, numeral 6 indicates the optic portion, and numeral 7, 7xe2x80x2 is the haptic portion. In the form of the haptic portion of a one-piece type intraocular lens, an angle of approximately 5 to 10 degrees is provided in many cases as shown in FIG. 8, like the above two-piece or three-piece type intraocular lens.
Further, as far as the form of the haptic portion is concerned, there is an intraocular lens called a wing type. FIG. 9 schematically shows a side view of an wing type intraocular lens. The haptic portion 7,7xe2x80x2 rises at an angle of approximately 5 to 10 degrees and then comes to be parallel with a plane at right angles with the optical axis of the optic portion. Intraocular lenses of all the types are designed such that the lenses inserted in capsules can be stably fixed in the capsules.
Further, it is known that the haptic portion of the above soft intraocular lens is also designed as a type provided with an angle of approximately 5 to 10 degrees or as a wing type.
Meanwhile, when an intraocular lens is inserted in a capsule, the inner diameter of the capsule shrinks to approximately 10 mm, and the haptic portion is accordingly compressed. Generally, the optic portion is supported by the function of the elastic force generated by the above compression of the haptic portion. In this case, part of the elastic force is transmitted to the optic portion. When the optic portion is formed of a hard material such as PMMA, almost no problem is caused by the transmission of the above elastic force. However, when the optic portion is formed of a soft material, depending upon how an intraocular lens is inserted in a capsule, the optic portion may be deformed or distorted, or the displacement of a lens may not be constant, due to the above elastic force transmitted to the optic portion, so that the resolution and lens strength may not be attained as designed.
Under the circumstances, it is a first object of the present invention to provide a one-piece type intraocular lens having an optic portion having an elasticity sufficient to be bent when the intraocular lens is inserted in an eye and a haptic portion which is like a haptic portion used in a conventional intraocular lens formed of PMMA and is for holding and fixing the optic portion in the eye and which is not easily removable.
Further, it is a second object of the present invention to provide a process for efficiently producing the above one-piece type intraocular lens free of a variability in product quality without requiring any complicated steps.
Further, it is a third object of the present invention to provide a soft intraocular lens whose optic portion is deformed or distorted in almost no case when the haptic portion thereof is compressed due to the shrink of a capsule after the soft intraocular lens is inserted in the capsule.
The term xe2x80x9chaptic portionxe2x80x9d in the present specification refers to a plurality of members extending from the optic portion as shown, e.g., in FIG. 4, and is used in this sense throughout the specification.
The present inventors have made diligent studies to achieve the above objects, and have found that the above first object can be achieved by a one-piece type lens having an optic portion and a haptic portion, said optic portion being formed of a copolymer obtained by polymerization of a monomer mixtures containing 2-[2-(perfluorooctyl)ethoxy]-1-methylethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, alkyl (meth)acrylate of which the alkyl group has a specific number of carbon atoms and a crosslinking monomer in a predetermined amount ratio and said haptic portion being formed of PMMA.
It has been also found that the above second object can be achieved as follows.
The above one-piece type lens can be easily and efficiently produced without a variability in product quality by polymerizing the above optic-portion-forming monomer mixture with keeping the monomer mixture in contact with a haptic-portion-forming material containing PMMA, or polymerizing a haptic-portion-forming monomer containing methyl methacrylate with keeping the haptic-portion-forming monomer in contact with an optic-portion-forming material formed of a copolymer obtained by polymerization of the above monomer mixture, to integrate the optic-portion-forming material and the haptic-portion-forming material, and cutting and polishing the integrated product.
Further, it has been found that the above third object can be achieved by a soft intraocular lens whose haptic portion is provided with a bendable portion which can absorb at least part of an external compressive force exerted on the haptic portion by deformation so that the bendable portion can decrease the force to be transmitted to the optic portion.
The present invention has been completed on the basis of the above findings.
That is, according to the present invention, there is provided a one-piece intraocular lens having an optic portion which functions as a substitute lens for a crystalline lens and a haptic portion for fixing and holding the optic portion in a predetermined position in an eye, the optic portion being formed of a copolymer obtained by polymerization of a monomer mixture containing
(a) 5 to 20% by weight of 2-[2-(perfluorooctyl)ethoxy]-1-methylethyl (meth)acrylate of the formula (I), 
wherein R1 is hydrogen or methyl,
(b) 40 to 70% by weight of 2-phenylethyl (meth)acrylate of the formula (II), 
wherein R2 is hydrogen or methyl,
(c) 25 to 50% by weight of alkyl (meth)acrylate of the formula (III), 
wherein R3 is hydrogen or methyl and R4 is a C4-C12 linear, branched or cyclic alkyl group, and
(d) 0.5 to 5% by weight, based on the total amount of the components (a) to (c), of a crosslinking monomer,
the haptic portion being formed of polymethyl methacrylate (the above intraocular lens will be sometime referred to as xe2x80x9cintraocular lens 1xe2x80x9d hereinafter).
According to the present invention, further, there is provided a process for the production of a one-piece intraocular lens having an optic portion which functions as a substitute lens for a crystalline lens and a haptic portion for fixing and holding the optic portion in a predetermined position in an eye, the process comprising polymerizing an optic-portion-forming monomer mixture containing 5 to 20% by weight of 2-[2-(perfluorooctyl)ethoxy]-1-methylethyl (meth)acrylate of the above formula (I), (b) 40 to 70% by weight of 2-phenylethyl (meth)acrylate of the above formula (II), (c) 25 to 50% by weight of alkyl (meth)acrylate of the above formula (III) and (d) 0.5 to 5% by weight, based on the total amount of the components (a) to (c), of a crosslinking monomer, with keeping the monomer mixture in contact with a haptic-portion-forming material containing polymethyl methacrylate, or polymerizing a haptic-portion-forming monomer containing methyl methacrylate with keeping the haptic-portion-forming monomer in contact with an optic-portion-forming material formed of a copolymer obtained by polymerization of the above monomer mixture, to integrate the optic-portion-forming material and the haptic-portion-forming material, and cutting and polishing the integrated product.
Further, according to the present invention, there is provided a soft intraocular lens having an optic portion formed of a deformable soft material which functions as a substitute lens for a crystalline lens and a haptic portion which is formed of arm-like two members extending outwardly from circumferential portions of the optic portion and is for fixing and holding the optic portion in a predetermined position in an eye, the haptic portion being provided with a bendable portion which, when a compressive force is externally exerted on the haptic portion so as to move at least any site of the haptic portion toward the optic portion, can absorb at least part of the external compressive force by deformation and decreases the force to be transmitted to the optic portion (the above soft intraocular lens will be sometimes referred to as xe2x80x9cintraocular lens 2xe2x80x9d hereinafter).
In the present invention, the term xe2x80x9c(meth)acrylatexe2x80x9d includes acrylate and methacrylate.